Process for the manufacture of noncurling films



Patented Jan. 28, 1941 UNITED? STATES.

PATENT OFFICE rnocnss FOR, 'rnn MANUFACTURE or NONCURIJNG mus Gerhard Hinz, Berlih-Schoneberg, Germany, as-

signor to Sherka Chemical (la-Ina, Bloomfield, N. J., a corporation of New York No Drawing. ApplicationMay 31, maserial No. 211,075. In Germany June 1, 1937 8 Claims.

' softening agents, nonsolvents and so on on each side of the-film 'is difierent and stresses occur in the film which cause the curling.

Attempts have already been made in various 7 ways to remove these stresses. For example the film has been subjected uniformly on both sides to the action of "solvents and the acticn interrupted beforethe film has become strongly attacked (French Patent No. 558,258). An attempt has. also been made to avoid the curling in such a manner that thefilms have been dried on both sides at diflerent temperatures vby means of .heated metal cylinders (English Patent No.v

436,784) These processes have, however, had no commercial succes.

The subsequent action of solvents in liquid or vapour form is certainly suited in principle to the avoidance-of stresses in the film, but the effect must be controlled. There is,;in particular,

the danger that the mechanical properties of the film may suffer on this treatment sincethe film becomes swollen to a considerable extent.-

In the following a treatment according to the present invention is described which with complete preservation of the film allows of the rernovalof the stresses produced on casting and thereby also the curling of the film. 'For this purpose the film is treated on both sides with difierent solvents and indeed with solvents which only possess a limited solvent capacity for the film, the air side being more stronglyswollen or dissolved. The selection of the solvent depends upon the conditions under which the film.v has" been cast. If in the casting one side has been particularly strongly heated then alsothe solvent capacity of the solvent employed, for the diiferent sides must difler considerably. The adjustment of the solvent capacity of the solvent must take place very-carefully and is best attainedby suitable combination o f a solvent with a nonsolvent. For the casein which oneof the two components is of low boiling point care must betakenthat' the solvent capacity of the solvent does. not change due to'fra'ctional evaporation of -one com. 55 ponent. This can be'attained for example in such a manner that the solvent mixture is maintained at as low a temperature as possible or that by circulation by pumping'with the addition of the more rapidly evaporating constituent, it is maintained at the desired composition, 5 The wetting with the solvent can take place by dipping of one side of the film over rollers or also by rinsing. Thereupon the film can for example by means of warm air be uniformly dried on both sides. v 1 In the case of such films as for photographic purposes for the purpose of the so-called substrating must have a gelatine intermediate layer, the above process can in practice be combined in one working operation with the coating with 15 gelatine in such a manner that the gelatine with addition of small quantities of gelatine solvent is dissolved in asuitable solvent mixture. 7 The following "examples illustrate the invention: 2

Exafiflle 1.

A cellulose triacetate film with a strongtendency to curltowards the wheel side is .treated as follows: the wheel side is rinsed with a solvent 25 'mixture wh ich contains6l volumes per cent of methylene chloride and 39 volumes per cent of methanol, whereas the air side istreated with a.

mixture which contains 70.5 volumes per cent of methylene chloride and 29.5 volumes per cent of 30 methanol. The temperature of the mixture is' maintained at 15 0.; the. speed of running through of the film amounts to 5 metres per minute. Example 2 35 Gelatine is-s'welled in about 4 times the quantity of water, the swollen gelatine dissolved in glacial acetic acid and subsequently methylalcohol added. A film of nitrocellulose is coated with 0 this solution in such amanner that for the wheel side the solution contains, 0.5% gelatine, 2% water, 48% glacial acetic acid and 50% methyl alcoholand for the air side 0.5% gelatine, 2% water; 28% glacial aceticacid, methyl 48 alcohol.

By the term swelling agents? as usedherem it is intended to cover -not only those agents the solventpower of whichjis insufiicient to more than just cause swelling of the film, but the term-" I used be capable of aflecting thefilm but inca- 55 pable of dissolving it under the conditions of the treatment. j

What I claim is:

1. The method of treating films from cellulose triacetate for the purpose of rendering the same noncurling comprising treating the wheel side of the film with an about 6:4 mixture of methylene chloride and methanol and-the air side of the film with an about 7:3 mixture of methylene chloride and methanol, followed by drying the film. t

2. Method as claimed in claim 1 in'which the film is treated continuously at the rate of about 5 metres per minute.

3. The method of treating a film of nitrocellulose comprising coating the same on the wheel side with a solution containing 0.5% gelatine, 2% water, 48% glacial acetic acid and 50% methyl alcohol and on the air side witha solution containing 0.5% gelatine, 2% water, 28% glacial acetic acid and methyl alcohol, followed by drying the film.

4. A method of treating films obtained from high molecular weight film-forming cellulose esters for the purpose of rendering the same noncurling which comprises treating the air side of said film with a mixture of solvents and nonsolvents and also treating the wheel side thereof with a mixture of solvents and nonsolvents, the mixture applied to the air side having the greater solvent power, and thereafter drying said film.

5. A method of treating films obtained from high" molecular weight film-forming cellulose triesters for the purpose of rendering the same noncurling' which comprises treating the air side of said film with a mixture of solvents and nonsolvents and also treating the wheel side thereof with a mixture of solvents and nonsolvents, the mixture applied to theair side having the greater solvent power, and thereafter drying said film.

6. A method of treating films obtained from high molecular weight film-forming cellulose triacetate for the purpose of rendering the same noncurling which comprises treating the air side of said film with a mixture of solvents and nonsolvents and also treating the wheel side thereof with a mixture of solvents and nonsolvents, the mixture applied to the air side having the greater solvent power, and thereafter drying said film.

'7. A method of treating films obtained fromhigh molecular weight film-forming cellulose triacetate forthe purpose of rendering the same said film with a mixture of solvents and nonsolvents and also treating the wheel side thereof I with a mixture of solvents and nonsolvents, the

mixture applied to the air side having the greater solvent power, one of said mixtures containing gelatine dissolved therein to provide-a gelatine layer on the emulsion side of said film, and thereafter drying said film.

GERHARD .HINZ. 

